1. Field of the Invention
The present invention broadly pertains to the separation of mineral substances. More particularly, the present invention pertains to the effective recovery of resins from resin-bearing coal through the application of centrifugal force.
2. Background of the Invention
Efficient and effective recovery or separation of one solid mineral substance from another has long presented problems. This is particularly true in the recovery of resins from resin-bearing coal. Certain coal deposits, such as those of the Wasatch Plateau and Book Cliffs fields of Utah, contain a substantial quantity of natural fossil resins which, in a purified condition, has utility in adhesives, coatings, printing inks, synthetic rubber compositions, traffic marking compounds, water proofing agents and the like. However, the resin, as it occurs in nature, is intimately admixed with the coal and the problem of separating it from the coal economically and on a commercial scale has presented serious difficulties to the art.
In its natural state, the resin occurs in small lumps, lenticular masses and in fracture planes of various thicknesses within the coal seams. Numerous investigators have demonstrated the fossil resins are considerably more friable than the coal with which they are admixed. When the coal is removed in the course of customary mining procedures, the majority of the recoverable resin is released by the fracture of the coal along the resin planes and by the tumbling action of the coal handling machinery which dislodges resinous particles adhering to the coal particles. A large portion of the recoverable resin is thereby liberated from the coal in the course of ordinary handling so that additional crushing of mine-run coal is not normally required to enhance resin recovery. Certain investigators, however, have cited the necessity for crushing coal to specified screen sizes for optimal resin recovery when employing certain recovery techniques. The added crushing step detracts from the economy of such techniques.
It is known in the art that resins may be separated from coal by means of froth flotation, air-lift flotation, float/sink separations employing inorganic salt solutions, and the like. None of these procedures, however, is capable of producing a high-purity resin concentrate. As well, most of the prior art processes for separating resin from coal are economically infeasible because they fail to satisfactorily resolve three basic problems, namely (1) since these resins are more dense than water, they cannot be effectively separated in quiescent water due to the lower specific gravity of water, (2) a high-purity resin concentrate cannot be effectively separated from the coal in agitated or upward flowing classifying systems, however slight the agitation, due to the contamination of the resin concentrate by appreciable quantities of coal fines and slimes, and (3) float/sink separations using aqueous solutions of inorganic salts are impractical because of the large volumes of salt solutions to be handled, the product and co-product contamination, the salt losses incurred, and the not inconsiderable environmental pollution problems associated with the waste solution disposal.
In U.S. Pat. No. 1,773,997, issued to Green, there is disclosed the separation of resin by a froth flotation process using one of several flotation agents to help separate the resins from the coal. While variations on this method are in commercial application today, the resin concentrate product so obtained is relatively impure, seldom, if ever, exceeding 50 weight percent resin, and with up to 40% by weight or more sorbed moisture. The resin concentrate obtained by such flotation procedure is so impure that it must be further refined as by solvent extraction, and the drying and solvent refining of such an impure resin concentrate is both tedious and economically disadvantageous.
In U.S. Pat. No. 2,378,152, issued to Nagelvoort, it is disclosed that wetted coal can be separated from unwetted resins using either upwardly flowing suspensions or air agitation. However, the resin concentrate of the disclosed invention is also relatively impure, containing only about 60% resin, and requires still further refining.
U.S. Pat. No. 2,409,216, issued to Lee, discloses an improvement on the refining of resin using a basic froth flotation process by heating the froth flotation concentrate to the order of 250.degree. to 300.degree. C. in order to melt the concentrate, following which a solvent refining process may be employed.
U.S. Pat. No. 2,506,300, issued to Klepetko et al., seeks to circumvent the unsatisfactory performance of froth flotation and other prior art processes for preparing fossil resin concentrates by employing a continuous solvent leaching and extraction process. However, because of the large quantities of coal fines which must be handled and the necessity for desolventizing and drying the coal fines and slimes, this process is economically disadvantageous and has never achieved successful commercial implementation.
In U.S. Pat. No. 2,506,301, issued to Klepetko et al., there is disclosed a flotation process not employing flotation agents or wetting agents and using air-lift flotation in place of mechanical agitation. This process tends to minimize crushing and attrition of the friable resin particles present in mechanically agitated flotation processes. The process demonstrates an improved recovery of larger sized resin particles, i.e., 28.times.100 mesh, over that in conventional mechanical systems, but still provides an impure flotation product which admittedly requires still further refining, e.g., by solvent refining.
In U.S. Pat. No. 2,591,830, issued to Klepetko et al., again it is sought to circumvent the unsatisfactory performance of froth flotation and prior art processes and the economic infeasibility of direct solvent refining processes by preparing resin concentrates using a basic sedimentation technique combined with a frothing agent which assists the collection of resin particles at the surface of the sedimentation tank. While the method is simpler than the froth flotation process, the quality of resin concentration is not significantly improved. The concentrate may contain a somewhat higher percentage of non-resin contaminants than a concentrate, e.g., produced in a specially built flotation plant, but it is stated that the concentrate is readily amenable to refining by solvent extraction.
In U.S. Pat. No. 3,637,639, issued to Zinniel et al., still another process is described for the continuous solvent extraction of resin from coal. This process employs special extraction and recovery equipment and accomplishes the primary segregation of coal fines from solutions of the resin dissolved in suitable organic solvents by means of liquid cyclonic separators in a classical two phase (solid coal/resin solution) separation. However, the process is laborious, equipment intensive and relatively quite expensive to operate.
Accordingly, it is an object of the present invention to provide an improved method for separating or recovering one solid mineral substance from another solid mineral substance, and in particular, an improved method for recovering a resin concentrate from resin-bearing coal. The provision of particular apparatus for carrying out the improved process is also an object of the present invention.
Another object of the present invention is to provide a method for recoverying a high-purity resin concentrate from resin-bearing coal, which resin concentrate is suitable for use without any further refining.
Still another object of the present invention is to provide an improved method for recovering resin from coal without concern as to the particle size of the coal material to be treated.
Yet another object of the present invention is to provide a most efficient and economically feasible method for recovering resins from resin-bearing coal.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description, the accompanying drawings, and the appended claims.